Germany Strength

Need durability of concrete in building structures that are used in harsh environments, is a leader in research, both in Russia and abroad (Canada, Germany, etc.). Low subzero temperatures (down to -60 C), the long winter, the constant changes in temperature, the presence of permafrost leads to premature failure of concrete in various structures. Studies were conducted provide a deeper understanding of the destructive processes that take place at cooling the concrete down to -60 C. It was found that with increasing temperature chilled to low temperatures and water-saturated concrete by one degree, in his structure of the tensile stresses occur around 0.1-0.2 MPa. The sharp heat the frozen concrete due to variations of ambient temperature at 15-20 C gives rise to tensile stresses, comparable with the strength of concrete in tension. Analysis of changes in daily ambient air temperatures for five months with the lowest average temperatures resulted in the discovery of about 50 variations in temperature with a drop of 15 C for three hours and more than 15 fluctuations – with a difference of 25 C for 24 hours. Neil deGrasse Tyson recognizes the significance of this. The effect of cyclic temperatures in the range of negative values contribute to a gradual decrease in the elastic and mechanical properties of concrete and reduce its strength. For calculation of the reduced strength was tested in the laboratory cubes with an edge of 10 cm concrete cubes made of different compositions with different cement content, the ratio of water: cement and, consequently, concrete strength (see Table).

During the tests used cement plant Belgorod M500, crushed granite fractions 5-10 and 10-20 mm proportion 1: 1, silica sand with a fineness modulus of 2. Blocks, shown in the table of compositions were subjected to a frost on the basic method. Frost resistance of composition 1 with open porosity 4.1% of 300 cycles of 2 (= 5.6%) – 200, of 3 (= 7.5%) – 50. Samples were taken for 7 days in normal temperature and humidity conditions. Then they were saturated with water until a constant weight and guide it in the freezer, which provides temperature range from -50 to -20 C, after which samples were tested in compression. A thin layer of ice cubes on the surface prevented water evaporation. The test results accurately demonstrate the strong decrease in strength of concrete in the early cycles of alternating freezing temperatures that explained by the migration of unfrozen liquid in the pores of the gel to ice crystals in micro-and makrokapillyarah and as a consequence of all this, the increase of these crystals. Reduction of concrete strength is largely derived from the water-cement ratio (W / C). Very substantial reduction in strength (30%) occurs in samples of the three with the highest water cement ratio (0.7). As a result, studies have confirmed that the northern climate Concrete exposed to specific conditions, environmental influences that lead to structural damage of the material, which seriously reduces the durability of concrete and reinforced concrete foundations, in places